Exhaust Gas Recirculation: Description and Operation

PURPOSE
The Exhaust Gas Regulator (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by decreasing combustion temperature. The main element of the system is the digital EGR valve. The digital EGR valve feeds small amounts of exhaust gas back into the intake manifold and then into the combustion chamber.

EGR CONTROL
To regulate EGR flow, the Powertrain Control Module (PCM) controls the EGR solenoids to vary the amount of EGR flow. The PCM uses information from the following sensors to regulate the solenoid:

^ Engine Coolant Temperature (ECT) sensor.
^ Throttle Position (TP) sensor.
^ Manifold Absolute Pressure (MAP).

RESULTS OF INCORRECT EGR SYSTEM OPERATION
With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:

^ Engine stalls after cold start.
^ Engine stalls at idle after deceleration.
^ Vehicle surges during cruise.
^ Rough idle.

Too little or no EGR flow allows combustion temperatures to get too high. This could cause:

^ Spark knock (detonation).
^ Engine overheating.
^ Emission test failure.